The accumulation of medical evidence in recent years regarding the adverse health implications of high fat diets, principally heart attacks, atheriosclerosis and overweight, has caused consumers to become extremely concerned about their diets. It is estimated that between 70-80% of U.S. adult females follow a weight reducing diet at least once a year. Men are also concerned about their weight and cholesterol levels. The concerns of both men and women have given rise to diet fads, diet drinks especially in the soft drink, wine and beer industry, and exercise programs and health clubs.
Common obesity is one of the most prevelant metabolic problems among people today. Fats and oils are necessary for balanced nutrition. However, the average consumer simply consumes more than is needed for proper nutrition. Fat, at 9 calories per gram, as compared to 4 calories per gram for carbohydrates or proteins, is the most concentrated dietary energy form. It is estimated that fat constitutes about 40% of the total calories in the typical western diet. Fats are consumed directly in meats, spreads, salad oils, and in natural produce such as nuts and avocados. Fats and oils are consumed as a result of absorption or incorporation in the foods during baking and frying. The vast increase in consumption of fast foods is a major contributor to the increase in the amount of dietary fat since fast foods rely extensively on frying processes employing fats and oils. In addition, the snack food industry uses large amounts of fats and oils in the production of potato chips, corn chips and other snack items. For example, in 1981 the USDA estimated approximately 12 billion pounds of fat and oil were used in edible products, predominately baking, frying fats, margarine, salad oil and/or cooking oil.
There is thus a clear indication that there is an enormous potential health food market for a fat substitute or fat mimetic that is either entirely non-digestible, or has reduced caloric value. Many nutritionists believe that Americans typically rely on fats for too large a proportion of calories in their diet. The National Research Council, for example, has recommended that Americans reduce the proportion of their dietary calories coming from fats from 40% to at least 30%. Replacement of fats in the diet with non-caloric substitutes is a more efficient way of reducing caloric intake than replacing sugar or carbohydrates because gram for gram, the substitution of non-caloric fat substitutes is more than twice as effective than reducing carbohydrate content with such things as saccharine or Nutra-sweet.
One of the difficulties in eliminating fat from the diet is the fact that fats and oils are all-pervasive in food products. In part, this is because they play an important role in the organoleptic acceptability of food products. For a fat substitute to be acceptable, it must be non-digestible, that is, not hydrolyzed in the digestive tract. In addition, it should not be directly absorbed through the intestinal wall. While some types of fat substitutes may be non-digestible, they are not of sufficiently high molecular weight to prevent them from being absorbed through the intestinal wall. The threshold molecular weight of non-absorbability for lipophilic molecules appears to be about 600.
In addition, the fat substitute must itself be non-toxic at high levels of ingestion. It must contain no toxic residues or impurities. To the extent that a fat substitute may be partially hydrolyzed in the digestive tract, any hydrolysis products must be non-toxic and/or metabolizable. If metabolizable, they should have very low caloric value. In general, fat substitutes must be without any serious medical side affects.
The fat substitutes must also have good organoleptic qualities of mouth feel and have no taste. In addition, fat substitutes must have appropriate physical properties for use in food compositions. That is, they should be liquids or solids depending on whether they are used as oil or shortening substitutes, and where used for cooking, must be thermally stable. While certain polysaccharide gums have been used as thickening agents, bulking agents or fillers in low-calorie foods, they can give a product a "slimy" mouth feel and are unsuitable for cooking as they have no thermal stability.
Acceptable synthetic fats would be added in large quantities (30-60%) to salad oils, cooking oils, margarines, butter blends, mayonnaise, shortenings and the like to create a new class of low-calorie products. While "low calorie" mayonnaise and salad dressings are presently available, the reduction in calories is achieved by increasing the water content with a corresponding loss in the organoleptically "rich" taste of such products.
A current review of the field is found in a feature article entitled "Getting The Fat Out-Researchers Seek Substitutes For Full-Fat Fat" JAOCS, Vol. 63, No. 3, (March 1986) pp. 278-286, 288.
One prior art proposed fat substitute is sucrose polyester (SPE), shown in U.S. Pat. Nos. 3,600,186 (Matson, et al. 1971), 3,251,827 (Scheil et al.) and 3,963,699 (Rizzi, et al., 1976). The SPEs are produced by the reaction of a monosaccharide, disaccharide or sugar alcohol having a minimum of four hydroxyl groups with fatty acids having from 8-22 carbon atoms. It was reported in "Chemical and Engineering News" (Jul. 26, 1982, page 32) that incorporating SPE as a partial replacement of the fats in the diets of ten obese patients dropped their caloric intake while satisfying their perceived need for fats. An additional benefit was the lowering of serum cholesterol, low density lipo-protein and triglycerides, all of which have been implicated in artery hardening diseases. However, SPE has the serious disadvantage of causing diarrhea, and plasma vitamin A and vitamin E levels are decreased.
The process for production of SPE is basically a methanolysis followed by esterification and extraction. The SPE process requires long reaction time with alternating additions of fresh transesterification catalyst and excess methyl soybean fatty acid ester (RCO.sub.2 Me). Temperature control is critical because sucrose will char at its melting point of 185.degree. C. Further, in order to solubilize sucrose in the esterification solution, it must be added slowly as a micron-sized powder (produced by reduction of sucrose crystals in a hammermill) to a solution of RCO.sub.2 Me containing half as much alkali metal soap as sucrose. After the sucrose is partially esterified, excess RCO.sub.2 Me is added and the mixture heated at 145.degree. C. for 8-12 hours. The fatty ester starting material, RCO.sub.2 Me, is not made in a continous process. Rather, it is made in a batch process and must be washed with water to recover all the glycerol. Commercial cane sugar must be reduced to a consistency of fine talcum powder, on the order of 50 microns or below in order to promote its dissolution in the reaction solution. Two stage addition of RCO.sub.2 Me is necessary to prevent disproportionation to sucrose, which will char, and sucrose higher esters. For each pound of SPE made, one pound of RCO.sub.2 Me must be cleaned up and recycled. Because a large excess of RCO.sub.2 Me is used, the isolation of SPE is a complex process necessitating liquid-liquid extractions at OC with methanol or ethanol to remove unreacted RCO.sub.2 Me. A final extraction with hexane and clay bleaching is necessary to produce a light-colored product. The major yield loss occurs during the purification process.
U.S. Pat. No. 3,521,827 discloses a preparation of SPE by means of a solvent-free interesterification using phenyl esters. However, phenol is liberated during the reaction. Since phenol is extremely toxic and caustic, it contaminates the product and is very difficult to separate. Accordingly, this process did not prove satisfactory for synthesis of SPEs for the food industry. U.S. Pat. No. 3,963,699 calls for solvent-free transesterification involving heating a mixture of the polyol containing four hydroxyls, fatty acid lower alkyl ester, and alkali metal fatty acid soap in presence of a basic catalyst to form a homogenous melt, and subsequently adding to the reaction product of that heated mixture excess fatty acid lower alkyl esters to obtain the SPE.
U.S. Pat. No. 4,034,083 also to Proctor and Gamble discloses fortification of the SPEs with fat-soluble vitamins to form pharmaceutical compositions for treating or preventing hyper-colesterolemia in animals, and for use in low calorie foods. This mixture is required because eating SPE causes vitamin depletion as noted above.
U.S. Pat. No. 3,818,089 indicates that the C.sub.12 -C.sub.18 ether analogs of glycerides, glycerine alkyl ethers are not digestible.
As shown in C. U. Werl et al, Food Cosmet. Toxicol., 9 (1971) p. 479, monopropylene glycol (MPG) can be ingested with no harmful effects. It is metabolized by the same metabolic pathways used by carbohydrates. MPG is currently used as a humectant in shredded coconut and in moist cake mixes. Ethylene oxide and propylene oxide-based food additives, such as propylene glycol mono-stearate, are recognized food additives, with allowable limits being prescribed by code.
Booth, A., and Gros, A., in a paper entitled Caloric Availability and Digestibility of New-Type Fats, Journal of the American Oil Chemists Society, Vol. 40, October 1963, pp. 551-553, disclose that in rat feeding studies amylose palmitate, amylose stearate and amylose oleate are only 17-29% digested. A related prior paper of Gros, A., and Feuge, R., entitled Properties of the Fatty Acid Esters of Amylose, Journal of the American Oil Chemists Society, Vol. 39, January 1962, pp. 19-24 discloses that these esters do not have sharp melting points and are extremely viscous when melted. The densities were somewhat greater than those of corresponding free fatty acids and glycerides. While the interest was for use as dip-type coatings in both foods and non-foods, no information appears to be available concerning the ability of these compounds to mimic sensory and functional properties of triglyceride fats in foods.
Mangold and Paltauf extensively reviewed ether lipids in their book Ether Lipids, Academic Press 1983. They report that trialkyl glycols having long alkyl chains are not hydrolyzed or absorbed when fed to rats. These long chain trialkylated glycols are reportedly non-toxic and do not interfere with absorption of fats and fat soluble vitamins. However, they are oxidized much more easily than normal fats having comparable acyl chains, so stability appears to be a problem. Further, these compounds are difficult and expensive to prepare.
Canadian patent 1,106,681 issued to Swift and Company in 1981 relates to dialkyl glycerol ethers which are absorbed only in small amounts when fed to rats. Blends are said to exhibit the physical and organoleptic properties of conventional fats.
U.S. Pat. No. 2,962,419 discloses esters of neopentyl type alcohols such as pentaerythritoltetracaprylate. The alcohols contain from 1-8 hydroxyl radicals and include at least one neopentyl nucleus while the fatty acids contain at least four carbon atoms. They were shown to be non-hydrolyzable by pancreatic lipase. Rats fed with these esters had lower levels of lipids in their serum. However, in demand feeding studies, rats which received these neopentyl alcohol esters ate more food than the control rats and thus there was no difference in weight gain among the two groups. Accordingly, it is possible that fat craving is stimulated by these compounds rather than satisfied.
Retrofats are esters of fatty alcohols with tricarboxylic acids. It is reported that they are not hydrolyzed by pancreatic lipase and thus may have potential as non-absorbable fat substitutes. However, increased stool bulk resulting from ingestion of the non-absorbable retrofats is reported to be a potential drawback.
Alkyl esters, such as dodecyl ester of 2,3-ditetradecyloxypropionic acid have been suggested as a fat substitute but were found to be metabolized and absorbed in in vivo rat study experiments. The alkyl ester group was split off first, followed by the alkyl ether groups.
As reported in JACS, Vol. 8 (1958) pp. 6338 ff and JAOCS, Vol. 36 (1959) pp. 667 ff, the USDA has synthesized a number of diglyceride esters of short chain dibasic acids for potential application in foods. Distearin glyceride esters of dicarboxcylic acids were found to be poorly digested and utilized by rats. Distearin adipate was almost completely non-digested while adipostearin was only 58% digested in rat feeding trials. In contrast, the oleostearin and dolein esters of dicarboxylic acids were more digestible and utilized. The symetrical diglyceride esters of fumaric, succinic and adipic acids are more viscous than cottonseed oil and coconut oil. These may have use as pan greases, slab dressings or surface coatings for foods.
U.S. Pat. No. 3,579,548 to Procter and Gamble in 1971 discloses uses of triglyceride esters of alpha-branched carboxylic acids as low calorie fats. These esters exhibited a coefficient of absorbability ranging from about 0-50 as compared to 90-100 for ordinary triglycerides. It is postulated that the alphabranched carboxylate structure prevents the compounds from being hydrolyzed by pancreatic enzymes. Proposed uses are as fat replacements in salad oil, mayonnaise, margarine and dairy products.
Polyoxyethylene stearate is an emulsifying agent with fat like properties that yields only 4.2 kcal/gram when ingested. The molecule is hydrolyzed to stearic acid which is metabolizable, and to polyoxyethylenediol which is excreted unchanged. The use of fat-like emulsifying agents as low calorie fat substitutes has been suggested in the literature.
U.S. Pat. No. 3,337,595, issued to Nalco Chemical in 1967, discloses a method of producing fatty acid esters of polyoxypropylated glycerol of the formula glycerol (propylene oxide).sub.n (fatty acids).sub.m, which from the molecular weight values in the patent result in n=9-16 and m=1 or 2. These esters are disclosed to be useful for controlling, suppressing and/or preventing foaming of aqueous systems having foaming tendencies in industrial processes. Illustrative types of aqueous systems are cellulosic suspensions involved in the manufacture of paper, sewage disposal systems, detergent containing systems, saponin-containing systems, protein containing systems and the like. 1,2-propylene oxide is adducted on glycerol to produce a polyoxypropylated glycerol (POG) with a molecular weight in the range of 600-1,000. Fatty acid esters are prepared by stoichiometric esterification of the POG with saturated or unsaturated alphatic monocarboxylic acids having chain lengths of 12-22 carbons. The esterification process occurs in the range of 200.degree.-240.degree. C. under a vacuum on the order of 30-50 mm mercury. Specific examples are directed to stearic acid diesters of polyoxypropylated glycerol having a molecular weight of 700. An emulsifier is required in the anti-foaming formulations, the specific examples being directed to polyoxyethylene glycol 400 di-oleate. The monocarboxylic acids used to form the diesters are those having C.sub.12-22 carbons. There is no specific disclosure of a triester or of complete etherification with propylene oxide. There is also no disclosure of the use of the diester compounds as fat substitutes in food products.
Gibson, U. H., and Quick, Q., in a paper entitled The Average Molecular Structure of Base-Catalyzed Low-Mole Adducts of Propylene Oxide to Glycerin, J. Applied Polymer Sci., Vol. 14 (1970) pp. 1059-1067 indicate that with a molar ratio of glycerin (G) to propylene oxide (PO) of 1:3, 63% of the adduct product will have all three hydroxyls propoxylated, with 1:4, 92% are propoxylated, and with a ratio of 1:5 all the original hydroxyls will be propoxylated.
It is clear that there is a great need in the art for improved fat substitutes that are easy to synthesize and do not have the disadvantages of the prior art proposed compounds.